I have been trying for an hour now and I just cant do it. I quicksave, shoot the grenade rifle at my feet and load but it just doesnt work. I tried loading when I heard the grenade explode, I tried loading before it. I just cant do it. Am I doing something wrong?

For speedcripple you need to quick load as it explodes. However 2-Handed weapons change your normal animation which removes the extra speed while you have the weapon equipped. Just un-equip or switch to a 1 handed weapon to see the effect.

However in New Vegas speedcripple is obsolete and not really needed for anything anymore :)

Thank you Radioactiv03, I can do it now.